1. Field of the Invention
The present invention relates to an information display apparatus, and more particularly to an information display apparatus which has a display area at least part of which is a liquid crystal display which uses liquid crystal with a memory effect, especially liquid crystal which exhibits a cholesteric phase.
2. Description of Related Art
In recent years, apparatuses which simultaneously display relatively unchangeable information such as an advertisement and changeable information such as news are demanded. In order to display information which changes at a high speed, a display which can write a picture thereon at a high speed must be used. Conventional displays of this type are a CRT display and a liquid crystal display which has TFTs (thin film transistors) for the respective pixels so that TN liquid crystal can be driven by an active matrix driving method. In such a display suitable for a motion picture, the whole screen is controlled for writing. More specifically, the whole screen is scanned in one direction at specified times for writing.
Such a conventional display which is suited to display a motion picture has a disadvantage of consuming great electric power. Also, a liquid crystal display using TFTs is expensive. When the display has a large number of pixels, it is very expensive. With respect to a CRT display, thinning of the display is difficult.
In the meantime, as a PDA or a portable terminal unit such as a portable telephone, a device which is small, light, easy to carry and consumes little battery to be usable for a long time is demanded. At present, however, than the body itself of such a device, its display section and electric source section consume greater electric power, which necessitates the use of a large volume of battery.
Thus, practical use of a display which consumes little electric power is demanded. The present inventors have developed displays using chiral nematic liquid crystal. Chiral nematic liquid crystal is bistable and has a memory effect. Accordingly, without application of a voltage, such a display can continue displaying a picture thereon, and it is possible to reduce the consumption of electric power. At present, in order to cause this kind of liquid crystal to make a phase transition, a relatively high voltage is necessary; therefore, a simple matrix driving method, not the active matrix driving method using TFTs, is adopted. Because the simple matrix driving method is adopted, even if the display has a large number of pixels, it is not expensive.
When chiral nematic liquid crystal is driven by a simple matrix driving method, however, it takes a relatively long time for writing on the whole screen. It is, therefore, difficult to display a motion picture on the whole screen of such a display when the screen has a large number of pixels.